<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box {
      width: 100px;
      background: lightcoral;
      border: 1px solid #000;
      /* display: flex; */
      /* display: inline-block; */
      /* position: absolute; */
      /* position: fixed; */
      /* float: left; */
    }
    .box1 {
      width: 100px;
      height: 100px;
      background: lightgreen;
      float: left;
    }
  </style>
</head>
<body>
  <div class="box">
    <div class="box1"></div>
  </div>
</body>
</html>